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From: taashlo@sandia.gov
Newsgroups: comp.lang.ada
Subject: How to Emulate C++ Macro with Static Local Variable?
Date: 24 Sep 2003 16:06:41 -0600
Organization: Sandia National Laboratories, Albuquerque, NM USA
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Date: 2003-09-24T16:06:41-06:00
List-Id: <comp.lang.ada>

Hello,

I'm trying to port a small C++ library to Ada95.  Most of it is going
quite well in that the Ada implementation is smaller, simpler, and
easier to follow than the C++ implementation.  But I've ran into a
hurdle with the following C++ construction:

class Test {
...
protected:
   struct s {
      int data[8];
   };
...
   void bar(s *t, int foo);
   #define BAR(foo_) if (1) { \
      static s t_; \
      bar(&t_, foo_);\
   } else ((void)0)
...
};

What happens is that when you do this:

BAR(10);

it expands to this:

if (1) {
  static s t_;
  bar(&t_, 10);
} else ((void)0);

This, in effect, creates a (hidden) static local variable for each call
to bar().  This static variable (actually a structure, t_) is used to
cache information for each unique call to bar() such that subsequent
calls from that location can be processed *much* faster.

For instance, the following code would create three of the hidden local
variables:

for (int i = 0; i < 55; ++i) {
   switch (wozit()) {
      case 1: BAR(10); break;
      case 2: BAR(20); break;
      case 3: BAR(30); break;
   }
}

The first time each BAR() is encountered, it does the full processing,
but subsequent calls to the *same* BAR() used it's unique cached
information and go much faster.

Any ideas on how I can achieve this with Ada95?

Thank you,

Tad